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- Andersen, J. L., et al.
(författare)
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Pleistocene Evolution of a Scandinavian Plateau Landscape
- 2018
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Ingår i: Journal of Geophysical Research - Earth Surface. - 2169-9003 .- 2169-9011. ; 123:12, s. 3370-3387
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Tidskriftsartikel (refereegranskat)abstract
- The origins and Pleistocene evolution of plateau landscapes along passive continental margins of the North Atlantic have been debated for more than a century. A key question in this debate concerns whether glacial and periglacial surface processes have substantially eroded plateau areas during late Cenozoic climatic cooling or whether the plateaus have mainly been protected from erosion by cold-based and largely nonerosive ice sheets. Here we investigate the Pleistocene evolution of a prominent plateau landscape in Reinheimen National Park, southern Norway. We estimate erosion rates across the plateau via inverse modeling of 141 new cosmogenic Be-10 and Al-26 measurements in regolith profiles and bedrock. We combine these results with sedimentological analyses of the regolith. In the vicinity of Reinheimen's regolith-covered summits, the combination of uniformly slow erosion (<10m/Myr) and near-parabolic slope geometry suggests long-term equilibrium with the presently active periglacial mass-wasting processes. Outside summit areas, erosion is faster (up to >50m/Myr), possibly due to episodic glacial erosion. Despite some indications of chemical alteration, such as grusic saprolite and small amounts of secondary minerals, the fine regolith comprises low clay/silt ratios and is dominated by primary minerals with no sign of dissolution. Together with our modeled erosion rates, this indicates that the regolith cover formed, and continues to develop, during the cold climate of the Late Pleistocene. Plain Language Summary Plateaus dissected by steep-sided valleys and fjords are common landscape elements within the mountains bordering the North Atlantic. Most of these plateaus have likely experienced millions of years of near-freezing temperatures and were repeatedly covered by ice sheets during recent glacial periods. Yet the imprint of cold-climate erosion processes on the plateau landscape evolution remains poorly understood. Here we investigate the Pleistocene evolution of an extensive Scandinavian plateau landscape in Reinheimen National Park, southern Norway. We measure cosmogenic nuclides within the surficial layers of rock and sediment on the plateau. The concentration of these cosmogenic nuclides reflects the erosion of the plateau landscape and thereby the impact of recent cold-climate surface processes. We find that erosion has influenced the plateaus within the latest glacial cycles. In the vicinity of the highest, sediment-clad summits, the plateau shape is determined by processes related to freezing and thawing of rocks and sediment, while the influence of erosion by glaciers and streams increases further downslope.
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| 2. |
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| 3. |
- Jansen, J. D., et al.
(författare)
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Erosion rates in Fennoscandia during the past million years
- 2019
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 207, s. 37-48
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Tidskriftsartikel (refereegranskat)abstract
- The widespread existence of cosmogenic nuclides accumulated in bedrock prior to the last glaciation demonstrates the limited erosional efficacy of the most recent Fennoscandian and Laurentide ice sheets. Yet the deeper history of erosion in these landscapes repeatedly blanketed by ice remains essentially unknown. Here we present the first comprehensive ice sheet-wide analysis of cosmogenic 10Be data (n = 953) from the Fennoscandian landscape. We find 64% of all sampled bedrock surfaces contain 10Be inheritance, including >85% of blockfields and tors, and >50% of ice-carved terrain, in addition to 27% of ice-transported boulders. Recent ice sheets scoured landscapes well beyond glacial troughs and nuclide inventories reveal a patchy legacy of erosional effectiveness that diminishes at high elevations, such that 89% (n = 55) of bedrock samples retain inheritance above 1600 m. We exploit this widespread nuclide inheritance in a Markov chain Monte Carlo-based inversion model to estimate long-term erosion rates and surface exposure histories from 113 paired 10Be–26Al bedrock samples. Nuclide inventories with or without inheritance convey equally important information about the erosional effectiveness of the last ice sheet. We define cosmogenic nuclide memory as the residence time of bedrock samples inside the nuclide-production window (≤2 m depth) where ∼ 80% of the total nuclide production occurs. The cosmogenic nuclide memory is set by mean erosion rate and varies from ∼10 ka for samples eroded >2 m during the last glaciation to > 1-Ma for the slowest erosion rates. We find that mean erosion rates are well constrained compared to the ratio of exposure to burial. The inclusion of bedrock erosion in our computations thwarts the capacity to constrain surface exposure history or identify former nunataks from paired 10Be–26Al data. Ice-carved surfaces reflect diverse erosion histories that are not straightforward to interpret from surficial morphology alone. Relative to the ∼10 mm/kyr benchmark for polar ice masses, we report point-based mean erosion rates that vary by more than three orders of magnitude, with glacial troughs and areal-scour terrain eroding at ∼1 to >100 mm/kyr, blockfields at 0.8–16 mm/kyr, and tors at 0.8–7.7 mm/kyr (5th–95th percentiles). © 2019 Elsevier Ltd
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| 4. |
- Egholm, M., et al.
(författare)
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PNA HYBRIDIZES TO COMPLEMENTARY OLIGONUCLEOTIDES OBEYING THE WATSON-CRICK HYDROGEN-BONDING RULES
- 1993
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 365:6446, s. 566-568
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Tidskriftsartikel (refereegranskat)abstract
- DNA ANALOGUES are currently being intensely investigated owing to their potential as gene-targeted drugs1-3. Furthermore, their properties and interaction with DNA and RNA could provide a better understanding of the structural features of natural DNA that determine its unique chemical, biological and genetic properties3,4. We recently designed a DNA analogue, PNA, in which the backbone is structurally homomorphous with the deoxyribose backbone and consists of N-(2-aminoethyl)glycine units to which the nucleobases are attached5-9. We showed that PNA oligomers containing solely thymine and cytosine can hybridize to complementary oligonucleotides, presumably by forming Watson-Crick-Hoogsteen (PNA)2-DNA triplexes, which are much more stable than the corresponding DNA-DNA duplexes5-7, and bind to double-stranded DNA by strand displacement5,8. We report here that PNA containing all four natural nucleobases hybridizes to complementary oligonucleotides obeying the Watson-Crick base-pairing rules, and thus is a true DNA mimic in terms of base-pair recognition.
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